isAnagram.java

public class Solution {

    static boolean isAnagram(String a, String b) {
        // Complete the function
        if( a == null || b == null || a.equals("") || b.equals("") )
            throw new IllegalArgumentException();

        if(a.length() != b.length()){return false;}
        a = a.toLowerCase();
        b = b.toLowerCase();
        //create map
        Map<Character, Integer> map = new HashMap<>();

        //populating frequencies
        for (int k = 0; k < b.length(); k++){
            char letter = b.charAt(k);

            if( ! map.containsKey(letter)){
                map.put( letter, 1 );
            } else {
                Integer frequency = map.get( letter );
                map.put( letter, ++frequency );
            }
        }

        //comparing frequencies
        for (int k = 0; k < a.length(); k++){
            char letter = a.charAt(k);

            if( ! map.containsKey( letter ) )
                return false;

            Integer frequency = map.get( letter );

            if( frequency == 0 )
                return false;
            else
                map.put( letter, --frequency);
        }
        return true;
    }